The archive of a German writer and anarchist Erich Mühsam (1878– 1934) is a significant but “unexplored” part of the manuscript collection of the A. M. Gorky Institute of World Literature of the Russian Academy of Sciences. I publish three letters of a German science fiction writer Paul Scheerbart (1863– 1915) to Mühsam and a postcard that Scheerbart sent to a German writer Hans Heinz Ewers. The letters to Mühsam record negotiations with publishing houses in Munich and Berlin about the publication of Scheerbart’s manuscripts (1909). In the postcard to Ewers, Sheerbart writes about the progress in his work on the perpetual motion machine that he tried to construct in 1908–1909. The letters are published in German with Russian translation and commentary. The introductory article gives an overview of Scheerbart’s life and career, the specificity of his works, their problematics and poetics and especially focuses on Scheerbart’s epistolary heritage. These letters are the token of friendship and professional collaboration of the two writers that is reflected in their mutual work on the unrealized project of publishing a satirical newspaper “Vaterland.” The IWL archives contain the unpublished manuscripts of Scheerbart and Mühsam related to this project as well. The history and the structure of the Mühsam archive is another aspect covered in the introductory article. Both Erich and Zenzl Mühsam were victims of totalitarian regimes. Erich was killed by the Nazis and his spouse Zenzl spent many years in Soviet labor camps. The history of the Mühsam manuscripts became intertwined with Zenzl’s life. That is why the article devotes space to Zenzl’s biography and attempts to answer the following questions connected to the archive: how did the manuscripts get to the Soviet Union? Why is the archive uncomplete? Finally, I discuss the publication history of Scheerbart letters from the IWL collection. Keywords: Paul Scheerbart, Erich Mühsam, Zenzl Mühsam, Hans-Heinz Ewers, letters, archive, IWL.